Even though pressure drop across perforations for clean fracturing fluids can generally be accurately predicted, it is not well understood for fracturing slurries. In this paper, two wellbore models-one transparent and one high pressure-were used to study the perforation friction pressure behavior of sand laden fluids. The transparent model constructed with cast acrylic allowed visual observation of fluid exchange in the "rat-hole" and flow patterns of the slurries in the wellbore and through the perforations. Critical velocity at which sand begins to screenout at the perforations was also determined. Tests were performed in the high pressure model varying gel concentration, sand concentration, proppant size, and perforation diameter to gather pressure drop data. The effect of the ratio of perforation diameter to the average proppant size on the sand screenout tendency at the perforation was also investigated.A correlation to predict the change of perforation coefficient due to proppant erosion was developed from the laboratory data.This paper presents a field procedure to better estimate the change of perforation coefficient during proppant stages for calculating the change of perforation friction.References and illustrations at end of paper 479 Incorporating this change of perforation pressure drop during proppant stages in the real-time bottomhole treating pressure calculation will enhance interpretation of the treatment analysis.
Borate-crosslinked fluids have increased in usage for fracturing treatments in recent years because of their low cost and low damage potential to formations. Until recently, most applications have been in shallow wells below 200°F because of high friction pressures and relatively low thermal stability. Recent advances in borate fluid chemistry have resulted in new techniques to minimize pumping pressure through the use of chemically delayed borate crosslinking agent.Ability to minimize friction pressure with delayed borate crosslinker has reduced treatment cost and extended the application of borate-crosslinked fluids in deeper wells with higher bottomhole temperature (to 300°F). Laboratory and field data have been gathered to investigate the effects of fluid parameters on the friction behavior of the delayed borate-crosslinked fluid.The laboratory experiments were performed with a recirculation flow loop to simulate field conditions, The field test was performed in a vertical wellbore. Measurements were made with three bottomhole memory gauges installed at various depths.References and illustrations at end of paper This paper presents friction pressure correlations derived from laboratory and field data for calculating realtime bottomhole treating pressure on-site to enhance the fracturing treatment analysis. Case histories are used to demonstrate the accuracy in friction pressure prediction for delayed borate-crosslinked fluids using the correlations presented in this paper. A method is also presented for field application of the friction pressure correlations provided in this paper.
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